The present invention relates to an improved chest drainage unit, having an increased airflow capacity, which both operates noiselessly and maintains the patient vacuum at safe levels in the event of failure of the device that regulates the amount of suction applied throughout the unit during its normal course of operation.
A chest drainage unit is an apparatus for suctioning gases and liquids from the chest cavities, or pleural cavities of patients. The pleural or chest cavity lies within the rib cage above the diaphragm and is surrounded by a pleural membrane. The pleural cavity contains both lungs, which in their normal expanded state fill the pleural cavity. Several conditions and diseases such as emphysema and various infections can cause a build up of liquid and gases around the lungs in the intrapleural space. When this happens, it causes the lungs to collapse to a volume much less than that of the pleural cavity, severely impairing breathing functions. The lungs can be re-expanded to their normal state of filling the pleural cavity by draining the liquid and gases from the area outside the lungs using a chest drainage unit.
Chest drainage units are also used in the treatment of patients who have air leaks in their lungs, allowing gases to enter the intrapleural space. Gases can be evacuated by use of a chest drainage unit. In treating patients with air leaks, it is very important to maximize the flow of air through the chest drainage unit, especially in the case of patients with high volume air leaks. Patients with broncho-pleural fistulae may have very large air leaks, particularly if the disease is associated with adult respiratory distress syndrome. For these patients, rapid and complete removal of the intrapleural air is necessary to prevent formation of a pneumothorax and to keep the pleural surfaces in contact, so that adhesion formation and eventual healing of the broncho-pleural fistulae may be enhanced.
There has therefore been a great need for a chest drainage unit having an increased airflow capacity while maintaining the ability to operate noiselessly and without risk to the patient of exposure to excessive negative pressure, i.e., suction. The anxiety-provoking nature of noise in a hospital environment has been appreciated for some time (see, e.g., "The Perceptual World of the ICU," Gowan, March-April, 1979 issue of Heart & Lung, Vol. 8, No. 2, pp. 340-344). Also, it is well known that exposure of the patient's chest cavity to excessive negative pressure can cause the patient both severe discomfort and severe damage.
U.S. Pat. No. 4,372,336, issued to Cornell et al. and assigned to Sherwood Medical Industries, Inc., discloses and claims a chest drainage unit similar to that of the present invention but for the improvements disclosed and claimed herein. The specification of the '336 patent in columns 1 and 2 discloses the prior art which existed with respect to chest drainage units a the time the application for the '336 patent was filed. This disclosure is incorporated herein by reference.
The chest drainage unit of the '336 patent comprises a collection chamber for collecting blood and other liquids suctioned from the patient's pleural cavity, an underwater seal chamber having a liquid seal which acts as a one-way valve for passing gases from the patient's pleural cavity to the atmosphere, a manometer chamber which provides an accurate indicia of the level of suction being applied to the cavity to be drained, a suction control chamber for limiting the maximum suction applied to the patient's pleural cavity, and a combination vent valve-and-filter assembly which permits the venting of negative pressure in the collection chamber by simple push button step to admit filtered air to the collection chamber.
One of the advantages of the chest drainage unit of the '336 patent over the prior art at the time the application for that patent was filed was the employment of a suction control chamber which did not involve the bubbling of atmospheric air through a liquid, and thus avoided the noise caused by such bubbling. In the preferred embodiment of the apparatus of the '336 patent, the suction control chamber comprises a housing comprising upper and lower compartments separated in part by a diaphragm. The upper compartment is in fluid communication with both the source of suction and the underwater seal chamber, while the lower compartment is in fluid communication only with the atmosphere. A nozzle which extends into the upper compartment has disposed in it a reduced diameter orifice through which air and gases from the patient's chest cavity pass, and through which the collection and underwater seal chambers communicate with the suction source. The nozzle is vertically movable toward and away from the diaphragm in order to regulate the vacuum to which the patient's chest cavity is exposed.
When set at a pre-determined distance away from the diaphragm, corresponding to a pre-determined vacuum level, the negative pressure on the diaphragm from the suction source causes the diaphragm to bow up and eventually contact the orifice, shutting off the vacuum. Eventually the downward, i.e. positive pressure on the diaphragm caused by the accumulation of gases in the upper compartment causes the diaphragm to move away from the orifice again, re-establishing communication between the suction source and the underwater seal chamber. The constant movement of the diaphragm in response to the suction source, and the vibrations of the diaphragm in response to the forces treated by the flow of gases through the upper compartment, causes some noise, which is sufficiently dampened by an appropriately sized and configured outlet port in the lower compartment allowing for communication between such compartment and the atmosphere. The outlet port is large enough to allow the diaphragm to move freely and yet small enough to dampen the noise caused by the movement of the diaphragm.
Another advantage of the apparatus of the '336 patent over the prior art at the time the application for that patent was filed was its "fail safe" mode of operation which prevents the patient from being exposed to dangerous levels of suction in the event of failure of the suction regulator to operate correctly. In the unlikely event that the diaphragm of the suction regulator were to tear or break, the small outlet port in the lower compartment of the regulator chamber would allow enough atmospheric air into the upper chamber to communicate with the suction source and maintain the negative pressure on the patient's chest cavity at a safe level.
In working to further improve the unit disclosed in the '336 patent, it was determined that for a given negative pressure of source vacuum, the airflow capacity is limited by the reduced diameter of the orifice of the nozzle through which the suction source communicates with the underwater seal chamber. The only way to increase the airflow in that unit is to increase the diameter of the orifice in the nozzle. This change, however, if incorporated, could pose significant operational difficulties as well as danger to the patient, because neither the noise damping nor "fail safe" devices of the '336 apparatus would be fully effective in the presence of the substantially increased airflow caused by the increased orifice diameter. Increasing the diameter of the orifice in the nozzle could adversely affect the "fail-safe" function, in that if the diaphragm of the suction regulator should break or tear, the atmospheric port in the lower compartment of the suction regulator may be too small to allow enough air to communicate with the suction source to maintain the pressure in the patient's chest cavity at a safe, comfortable level. Furthermore, increasing the flow of air through the chest drainage unit of the '336 patent would increase the noise caused by the vibration of the diaphragm to an unacceptable level, which could not be effectively dampened by the mechanisms provided for therein. In such a case, the outlet port in the lower compartment of the housing of the suction regulator would be too large to dampen the increased amount of noise.
Before the chest drainage unit disclosed in the '336 patent, the goals of noiseless operation and a reliable fail safe mode were deemed incompatible in the prior art in the presence of a substantially increased air flow. Although the chest drainage unit disclosed in the '336 patent functions very well, the need still exists for a chest drainage unit having an increased air flow capacity for the rapid and complete removal of pleural air, which both operates noiselessly and maintains safe patient vacuum levels at all times, even if the suction regulator fails to function.